1. Field of the Invention
The present invention relates to a photo-conductor plate and its manufacturing method, a surface emitting device and a liquid crystal display unit, and more particularly to the structure of a photo-conductor plate excelling in light transmittance when used as the front light of a liquid crystal display unit.
2. Description of the Prior Art
Usually, in a reflectance liquid crystal display unit using ambient light as the light source for displaying, its luminance is affected by the luminous energy of the ambient light, and therefore involves the problem that the visibility of the display extremely deteriorates in a dark place or any other environment where no sufficient ambient light is available.
Accordingly, in order to solve the above-noted problem, there is proposed a liquid crystal display unit of a type in which a front light (surface emitting device) is arranged on the front side of a reflectance liquid crystal display unit for use as an auxiliary light source. This front light-equipped liquid crystal display unit operates as a usual reflectance liquid crystal display unit in an environment where sufficient ambient light is available, such as outdoors in the daytime, and the front light is turned on as required to serve as a light source. A sectional structure of an example of such a liquid crystal display unit in which a front light is arranged on the front side of a liquid crystal display unit is shown in FIG. 8. This liquid crystal display unit 200 shown in FIG. 8 is configured of a liquid crystal display unit 220 and a front light 210, and the front light 210 is arranged on the front face (top face in FIG. 8) of the liquid crystal display unit 220 so that a photo-conductor plate 212 is arranged in the display area of the liquid crystal display unit 220.
The front light 210 is configured of a photo-conductor plate 212 formed by injection molding of transparent acrylic resin or the like and a light source 213 formed of a cold-cathode tube arranged on a side end face 212a of this photo-conductor plate 212. The bottom face (the side toward the liquid crystal display unit 220) of the photo-conductor plate 212 is used as a light emission face 212b from which light is emitted. The other face (the top face of the photo-conductor plate 212) than this light emission face 212b is used as a reflection face 212c where a first slope 216 and a second slope 217 ensuing from it, formed at an inclination with respect to the light emission face 212b, are alternately and periodically arranged to alter the direction of light within the photo-conductor plate 212. To the light emission face 212b of the photo-conductor plate 212 is stuck an anti-reflection film 215.
The liquid crystal display unit 220 has a configuration in which a first substrate 221 and a second substrate 222 facing each other with a liquid crystal layer 223 pinched between them are integrated by joining with a sealing material 224. On the side of the first substrate 221 toward the liquid crystal layer 223 are successively stacked a reflection layer 225, containing a reflection film for reflecting light having come incident on the liquid crystal display unit 220, and a display circuit 226 for driving and controlling the liquid crystal layer 223, and a display circuit 227 is provided on the side of the second substrate 222 toward the liquid crystal layer 223.
In the liquid crystal display unit 200 configured as described above, light emitted from the light source 213 is introduced into the photo-conductor plate 212 via the side end face 212a of the photo-conductor plate 212, propagates within photo-conductor plate 212 and at the same time is reflected by the first slope 216 having a greater angle of inclination with respect to the direction of light introduction to undergo a change in its propagating direction toward the light emission face 212b, eventually to be emitted from the light emission face 212b. This light emitted from the light emission face 212b comes incident on the liquid crystal display unit 220 as illuminating light, passes the display circuits 226 and 227 and the liquid crystal layer 223, is reflected by the reflection layer 225, returns to outside the liquid crystal display unit 220, and is transmitted by the light emission face 212b and the reflection face 212c of the photo-conductor plate 212 to reach the observer. In this way, the display on the liquid crystal display unit 220 is recognized by the observer.
However, the front light 210 of the liquid crystal display unit 200 configured as described above involves the problem that, as the anti-reflection film 215 is provided only on the light emission face 212b of the photo-conductor plate 212, contrast is reduced by reflection from either the inside or the surface of the photo-conductor plate 212. This is due to the reason explained below.
First, with the front light 210 described above, the light coming incident from outside on the reflection face 212c of the front light 210 is reflected by this reflection face 212c and directly reaches the observer to adversely affect his or her perception of the display.
Then, the light introduced from the light source 213 into the photo-conductor plate 212 via the side end face 212a of the photo-conductor plate 212 propagates within the photo-conductor plate 212. At the same time, its propagating direction is turned toward the light emission face 212b by the first slopes 216, steeper of the slopes 216 and 217 formed on the reflection face 212c, and about 96% of the light is emitted from the light emission face 212b to illuminate the reflectance liquid crystal display unit 220. However, about 4% of it is reflected by the light emission face 212b to become reflected light directed to the reflection face 212c, passes the reflection face 212c and is emitted outside to reach the observer. Such reflected light reaches the observer without passing the liquid crystal display unit 220, and therefore does not contribute to displaying. Therefore, this reflected light is perceived by the observer as noise, and contributes to the deterioration of contrast. Furthermore, as the reflected light is generated from the light reflected by the periodically formed first slopes 216 and passes the reflection face 212c on which the slopes 216 and 217 are periodically formed to reach the observer, it involves the risk of allowing moirxc3xa9 fringes to be generated by interference due to the periodicity of the slopes 216 and 217.
Next, as described above, the light from the light source 213, whose propagating direction is changed by the slopes 216 formed in succession periodically on the reflection face 212c of the photo-conductor plate 212, is emitted from the light emission face 212b to illuminate the reflectance liquid crystal display unit 220. The light coming incident on this liquid crystal display unit 220 is reflected by the reflection layer 225 of the liquid crystal display unit 220 toward the front light 210, and again comes incident on the photo-conductor plate 212. Part of the light traveling from this liquid crystal display unit 220 toward the front light 210 is reflected by the light emission face 212b and the reflection face 212c of the photo-conductor plate 212 to generate light which does not contribute to displaying but invites deterioration in contrast.
An object of the present invention, attempted in view of the above-described circumstances, is to provide a liquid crystal display unit equipped with a photo-conductor plate serving to enhance light transmittance by reducing reflection of light on its emission face and reflection face and a surface emitting device provided with this photo-conductor plate to be able to achieve efficient irradiation with light, and a liquid crystal display unit providing satisfactory contrast and excelling in displaying quality.
The above-stated object can be achieved with a photo-conductor plate provided with a substrate having a light emission face for emitting light introduced within via a side end face and a reflection face, positioned on the other side than the light emission face, for reflecting light propagating inside, and anti-reflection films provided over a surface of the substrate, wherein the anti-reflection films are provided over at least the light emission face and the reflection face.
It is preferable that a reflectance of the anti-reflection films is 1% or less of a reflectance of an Al film at an optical wavelength of 550 nm.
It is preferable that the reflectance of the anti-reflection films is 2.5% or less of the Al film in an optical wavelength range of 380 nm to 780 nm. It is further preferable that the reflectance of the anti-reflection films is 1.5% or less of the Al film in an optical wavelength range of 450 nm to 700 nm.
It is preferable that a refractive index of the substrate is not less than 1.48, and a refractive index of the anti-reflection films is not more than 1.35.
It is preferable that the anti-reflection films are formed by a dip coating process.
It is preferable that the anti-reflection films are a single-layered structure.
The above-stated object can also be achieved with a surface emitting device provided with a photo-conductor plate according to the invention and a light source arranged on an incident end face of the photo-conductor plate.
The above-stated object can as well be achieved with a liquid crystal display unit provided with the surface emitting device.